A class of machines exists in the art generally known as "scroll" apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the present invention is disclosed incorporated into a hermetic refrigerant compressor.
Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced approximately 180 degrees from the other. The scroll apparatus operates by orbiting one scroll member (the "orbiting scroll") with respect to the other scroll member (the "fixed scroll" or "non-orbiting scroll") to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation, i.e., the motion is purely curvilinear translation (i.e. no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus where a fluid inlet is provided, to a second zone in the scroll apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time, there will be at least one pair of sealed pockets, and when there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the scroll apparatus, the first zone being located at the outer periphery of the scroll apparatus.
The concept of a scroll-type apparatus has thus been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are relatively small and lightweight for a given capacity. They are quieter and more vibration free than many compressors because they do not use large reciprocating components (e.g. pistons, connecting rods, etc.), and because all of the fluid flow is in one direction with simultaneous compression in plural opposed pockets, there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relative low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination.
Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces ("flank sealing"), and area contacts caused by axial forces between the plane edge surfaces (the "tips") of each wrap and the opposite end plate ("tip sealing"). For high efficiency, good sealing must be achieved for both types of contacts, however, the present invention is primarily concerned with flank sealing. A positive flank load is necessary at all operating conditions to prevent scroll flank leakage. Flank load is a function of the operating conditions (i.e. pressure differential), scroll geometry, centrifugal loading and crankshaft "drive angle".
The drive of one popular type of scroll-type apparatus is radially compliant with the crank pin driving a drive bushing via a flat surface on the crank pin which slidingly engages a flat bearing surface disposed on an internal wall in the drive bushing. The bore in the drive bushing is slightly oval in cross-sectional shape to permit relative sliding movement between the crank pin and the drive bushing. While the scroll and crankshaft geometries are normally fixed to provide the minimum flank sealing at the specific operating parameters of a single machine, this scroll apparatus will be penalized when it is required to run at different parameters due to a change in its radial loading producing the flank sealing.
Thus, one of the problem areas of design in a scroll-type machine concerns the techniques used to achieve adequate flank sealing when a single machine is required to run under various operating parameters due to the fact that the scroll and crankshaft geometries for that machine are designed for a single set of parameters. An example of this problem of fixed design is in machines which are required to operate using 60 Hz power sources and those which are required to operate using 50 Hz power sources. If a scroll-type apparatus is designed for a 50 Hz (low speed) application, this apparatus would be penalized when running at 60 Hz (high speed) due to an increase in radial loading of the flanks. The penalties exacted in this case will be increased friction and excessive sound output or noise. If a scroll-type apparatus is designed for a 60 Hz (high speed) application, this apparatus may not achieve sufficient flank sealing when running at 50 Hz (low speed) due to a decrease in radial loading. A typical solution to the 60 Hz/50 Hz problem has been to have two different drive angle crankshaft/drive bushing combinations available for use depending on the specific application. This solution can be achieved by changing the drive bushing configuration and/or by machining variations of the flat on the crank pin of the crankshaft. Either of these solutions require significant additional investment in crankshaft tooling and gaging or in tooling for an additional drive bushing.
The present invention provides the art with a scroll type apparatus having a radial compliant drive. The radial compliant drive is achieved by using a set of corresponding flat drive surfaces with one of the drive surfaces being located on a drive bushing and the other being located on a crankshaft. The drive bushing is provided with a pair of flat drive surfaces with each flat drive surface of the drive bushing being capable of mating with the drive surface of the crankshaft in two different geometrical configurations to provide two different radial driving loads.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.